The sandwiches at Punpun in Darlinghurst might literally be life-changing. A nurse who handles organ transplants was the first to tell me about this cafe. It’s close to St Vincent’s Hospital, which means many other medical workers stop by. Punpun’s co-owner Lexy Allouche knows the heavy-duty responsibility of feeding them well and promptly.

“The amount of doctors out the front, staring at their watch [wondering], ‘Oh, how long is it going to be, because I’ve got to go do open-heart surgery?’ – it’s crazy,” she says. “Really crazy.”

Sure, there’s no hard data on whether Punpun’s coffee and sandwich selection leads to successful operations or in-patient happiness, but you might expect well-caffeinated (and well-fed) medical workers would be good for the health system.

It definitely has an impact on Allouche, who runs Punpun with her brother Lachlan. “What really hits me and Lachlan most is the hospital staff coming back every day,” she says. “Seeing them smile and having a good time … all the mayhem that we have to deal with behind the scenes, it makes it all worth it.”

The steamed-custard egg sandwich with chive mayo feels a next-level remix of the tamago sando in konbini stores.

The siblings opened this cafe in August, almost a year after selling St Kai in Mortdale. They wanted to do something more scaled back than their previous venture, which involved labour-intensive ramen and served more diners.

Originally, they planned to open something elaborate in Marrickville, styled after Japan’s beloved konbini (convenience stores), but they went with Japanese-style sandos (sandwiches) and sides in Darlinghurst instead.

You still detect that influence on Punpun’s menu. The steamed-custard egg sandwich with chive mayo, for instance, feels a next-level remix of the tamago sando in konbini stores.

Unlike the egg salad sandwich on the refrigerated shelves, this one is soft and thick, with the pillowy, padded smoothness of chawanmushi (Japanese egg custard). Order it with the optional chilli oil: the deep-red, spicy slick stains the spongey shokupan bread and enhances the contrast. Allouche uses jars of Lao GanMa and even has a shrine to this cult chilli condiment’s founder in the kitchen.

Punpun also stuffs thick slices of shokupan with a smashed beef patty, pickles and Tokyo Mac sauce: a take on the McDonald’s special sauce, seasoned with shichimi togarashi (a Japanese chilli spice blend) and other Asian flavours.

The P.P.F.C. is another burger-style sandwich, loaded with sesame-crusted fried chicken. If you prefer this crumbed protein as a stand-alone side dish, you can order it with hot honey or Kewpie mayo and curry salt. It’s a tribute to Famichiki, the chicken snack for which Family Mart konbini stores are famous.

This cafe happily acknowledges its love of Japan: its name comes from Inio Asano’s Goodnight Punpun manga series, and certain drinks (Pocari Sweat, Tea Craft’s sencha brew from Kyoto) and items of decor (like the Yuto Horigome skateboard deck) originate from there.

The coffee, however, comes from around the world via a range of specialty roasters, and is presented by barista Luke “Skinny” Willis (whose Signed By Skinny beans are brewed here, too).

He’s knowledgeable and welcoming and might pour you an interesting drop, like something grown by third-generation coffee farmer Ashok Patre on his Ratnigiri Estate in India and supplied here by DiggyDoo’s.

The milk toast evokes the staple served in Hong Kong’s cha chaan tengs (old-school Western-style cafes).

Allouche puts her “Aussie spin” on it – the bread is saturated with condensed milk so richly flavoured with Milo powder that it tastes like pure chocolate ganache.

It probably wasn’t what Thomas Mayne had in mind when he invented Milo in 1934 as an affordable health tonic to ward off malnutrition during the Great Depression – but it tastes amazing.

On the first of several visits to Punpun, I ordered the egg sando with a batch brew of the day. The stranger next to me did the same and yelled “great sandwich, great coffee!” as he left, a succinct and spot-on review. Sure, that didn’t exactly save lives, but there’s a quiet restorative power in a cafe simply doing things well.